Explosive events can be caused by either accidents or deliberate acts. Both of these are extremely dangerous to both people and structures. Engineers study the effect of explosive charges either in field tests or in laboratories. A prerequisite for the experimental investigation of blast effects and injuries, and the consequent development of protective technologies, is the ability to accurately, safely, and reproducibly simulate the air-blast loading conditions caused by an explosion.
Conducting experiments using actual high-explosive charges in field tests is problematic due to cost, availability of qualified sites and personnel, risk of accidents in storage, movement or setting of the charge, rate of testing, quality of extent of data gathering, inherent lack of reproducibility, poor control of the target setup conditions, and the inability to apply advanced instrumentation.
Since the 1800's, the use of laboratory testing has been popular to reproduce gas-dynamic shock waves in a safe and scientific manner. These early devices were versions of the modern gas-dynamic shock tube, which has a variety of uses, from experimental studies of supersonic aerodynamics to combustion. A standard shock tube uses a driver section of a circular cross-section having a constant cross-sectional area with axial distance known as a “conventional geometry.” Typically, any inclusions of area expansions in the circular cross-section are highly problematic to fabricate in a matter that would allow gradual and easily defined wall curvature, such that the area change with distance is smooth and gradual.
Scientists and engineers endeavor to use shock tubes to accurately and safely simulate blast conditions in a controlled and repeatable manner to research blast vulnerabilities of systems, detailed processes of blast loading, damages and injuries, as well as to develop countermeasures or protective technologies in a controlled, safe, economic and systematic manner. The shock tubes which accomplish this are called “blast simulators.”
A blast wave is a particular type of shock wave characterized by certain profiles or “wave shapes” for pressure, flow velocity, density, and temperature. In a blast simulator a shock wave generated from the “driver section” causes gas to pass through the shock tube to the “test section,” where experiments would be conducted, such as studies of blast damage to test articles measured by various devices.
Prior to the disclosed invention, there was a lack of blast simulators which accurately and efficiently replicated blast conditions for scientific investigations. While many have tried, previous blast simulators do not reproduce full and credible blast waveforms leading to the development of protection measures that may be ineffective or in fact deleterious when exposed to actual blast conditions.